Public Class ActivityStoppedState
    inherits ActivityState

    'Not from other state.
    Public Sub New(activity As IActivity, employee As IEmployee)
        Me.Activity = activity
        CurrentEmployee = employee
    End Sub

    'From other state.
    Public Sub New(state As ActivityState)
        Activity = state.Activity
        CurrentEmployee = state.GetEmployee()
    End Sub

    ''' <inheritdoc/>
    Public Overrides Function ActivityStateEnum() As ActivityStateEnum
        Return ProductiePitching.ActivityStateEnum.Stopped
    End Function

    ''' <inheritdoc/>
    Public Overrides Function GetEmployee() As IEmployee
        Return CurrentEmployee
    End Function

    ''' <inheritdoc/>
    Public Overrides Sub StartActivity(employee As IEmployee)
        If IsNothing(employee) Then
            'Nothing employee.
            Throw New Exception($"The employee can't be nothing when starting an activity from stopped state.")
        End If
        'Update employee.
        employee.CurrentActivity = me.Activity
        'Everyone can start this activity.
        Activity.State = New ActivityStartedState(Me, employee)
    End Sub
End Class